Single phase two-wire and three-wire system (difference)

In the wiring method from the transformer on a domestic power supply from
electric power company, that is, utility pole to each home, it has changed from
the single-phase two-wire system to the single-phase three-wire system.

..

It becomes impossible to correspond by two single phase line type by the
consumption of electricity's increasing in a recent home though two single phase
line type was natural in an old old house. Then, having appeared is a supply of
electric power method of the single-phase three-wire system.

Because the neutral line is grounded, the voltage of ground of the electric
wire becomes like 100V though 200V can be used for the single-phase three-wire
system. The voltage is high and no translation of danger especially.

Moreover, so in the single-phase three-wire system the
IH heater The appliance of 200V with large power such as (electromagnetic
cooker) and electric water heaters can be used. Because only half the current
flows in 200V with an equipment of the same power consumption compared with the
equipment of 100V, the high-power can be handled by even wiring for the same
thickness.

Then, the comparison calculation was theoretically done by two single phase
line type and the single-phase three-wire system. there was a difference of
which extent in the electric power transmission

Circuit of single phase two-wire and single-phase three-wire system

Figure
on this is two single phase line type, and figure below is a schematic diagram
of the single-phase three-wire system. I think that it is understood that two
single phase line type uses only partially 100 the V of the single-phase
three-wire system.

To compare it theoretically, I calculated in the single-phase three-wire
system with the current had been balanced.

It is assumed the one to use both of the load resistance of 100V of the two
resistance of 1k Ω as a simplified example. This is connected in parallel in two
single phase line type. The single-phase three-wire system connects it with 100V
for each as shown in figure. Moreover, resistance (R1,R2,R3,R4,R5) of each
electric wire is assumed to be 1 Ω by the thickness of the electric wire using
all the same things.

Then, the load resistance becomes 500 Ω in two single phase line type, and the
current of 0.2A flows. Power consumption becomes 20 a W in total. (Because the
power consumption of the electric wire is small, disregard it here. )

The current of 0.1A flows to each resistance in the single-phase three-wire
system. Power consumption becomes 10W because of each resistance, and becomes 20
a W in total.

Comparison of voltage descents with electric wire

The voltage descent with the electric wire of two single phase line type
increases to twice that of 0.2x1=0.2V, and becomes 0.4V in total. In a word, the
voltage that hangs to the load : It becomes 100-0.4=99.6V.

It is counterbalanced and the current doesn't flow because the current of
0.1A to which the phase shifts by 180 degrees will flow from both direction to
R4 when thinking about the voltage descent with the electric wire of the
single-phase three-wire system. Therefore, the voltage descent of 100V load
becomes 0.1x1=0.1V. In a word, the voltage that hangs to the load becomes
100-0.1=99.9V.

It is understood to become 1/4 in the single-phase three-wire system compared
with two single phase line type if the voltage descents with the electric wire
are compared. In a word, the single-phase three-wire system is that the voltage
descent with the electric wire it becomes 1/4 compared with two single phase
line type if it is the same electric wire, and the same electric power.

When the current doesn't flow to R4, and the voltage descent of R3 and R5 is
added, it becomes twice at 100V if it thinks about 200V circuit by the
single-phase three-wire system. It still becomes 1/4 in the single-phase
three-wire system compared with two single phase line type if it thinks at the
voltage descent rate because the voltage at this time becomes 200V.

It is necessary to compare the voltage descents here between 100V by the
translation to compare the methods of the single-phase three-wire system and two
single phase line type.

Comparison of power consumption with electric wire

Power consumption in the electric wire of two single phase line type
increases to twice that of 0.2x0.2=0.04W, and becomes 0.08W in total.

Power consumption in the electric wire of the single-phase three-wire system
increases to twice that of 0.1x0.1=0.01W, and becomes 0.02W in total.

It is understood to become 1/4 in the single-phase three-wire system compared
with two single phase line type if power consumption in the electric wire is
compared. In a word, the single-phase three-wire system is that generation of
heat of the electric wire it becomes 1/4 compared with two single phase line
type if it is the same electric wire, and the same electric power.

The single-phase three-wire system these are to the last in the state of the
ideal, and if the load doesn't do the balance, doesn't become it like this
either.

Notes of type wiring of three single phase lines

The type wiring of three single phase lines are two system 100V circuit, and
should arrange the load thinking about each current balance.

A voltage that is higher than 100V might hang in each load when the grounded
neutral line is disconnected. It is necessary to take care about the thing that
there is not loosening of the thing and the connection that doesn't put a fuse
in the neutral line especially.